1. Field of the Invention
The present invention relates to a driving cam of a geneva mechanism. As generally known, a geneva mechanism is constructed as follows. While a circular arcuate convex of a driving wheel and a circular arcuate concave of a driven wheel are coupled and sliding, the driven wheel is detained right at the place without rotating, and when a pin on the driving wheel is inserted into one of the slots of the driven wheel and then pulled out, the driven wheel is rotated to a predetermined degree.
It goes without saying that the transfer loss of energy is decreased, because the circular arcuate convex and the circular arcuate concave are sliding smoothly almost without any resistance.
2. Description of the Related Art
In the Japanese Utility Model Patent Laid-open No. 1985-64357, an art has been disclosed that the sliding resistance is reduced by disposing rollers successively in the circular arcuate convex.
In the above mentioned prior art, however, it is difficult to process an arrangement of the pins supporting the rollers in a complete round shape, and there is a defect of rather increasing resistance if an irregularity exists in arrangement of dthe rollers.
As opposed to the above described Publication, in the Japanese Patent No. 2788218, a mechanism holding balls(rotating bodies) inside a annular groove which is formed in a circular arcuate convex of divided wheel(driving rotating body) has been disclosed. However, a detailed structure of holding the balls is that, as shown in FIG. 9, after divided grooves 15A, 15B of having sections of about xc2xc of the circular arc are formed in the opposite surfaces of a pair of male and female cam members 11A, 11B, and then a annular groove 15 is formed by coupling a pair of cam members 11A, 11B with bolt 13, the balls 14 are held inside this annular groove 15 so as to be in contact with a circular arcuate concave 3(refer to FIG. 7 of the above described Publication).
However, firstly there are problems that the processing of matching the circular arcs precisely is very difficult when the annular groove 15 is formed by coupling, because the divided grooves 15A, 15B have to be formed individually, and the smooth rotation of the balls 14 can not be expected because the processing error is increasing. Secondly there are many causes to decrease processing accuracy such as of positioning of bolting hole because the divided grooves 11A, 11B are required to be assembled precisely without being displaced to the radial direction, when the male cam member 11A and female cam member 11B are coupled with bolt 13.
Accordingly, an object of the present invention is to provide a driving cam in which grooves of radial direction, which hold rotating bodies such as balls, can be formed precisely and have a good roundness, and smooth rotation of the rotating bodies can be guaranteed, and which does not affect the precision of the grooves formed in a radial direction when assembled.
To achieve the above object, in the driving cam of the present invention, a peripheral groove is formed concentrically with the driving shaft on a circular arcuate peripheral surface of a lacked circular plate core member, and rotating bodies disposed in the peripheral groove are hold by circular arcuate rims formed at the peripheral edge of covers which are attached to the top and the bottom of the core member.
Preferably, with a path of the rotating bodies being formed along the entire periphery, the rollers are cyclically rotated endlessly. The sectional form of the above described peripheral groove may be triangle, quadrangle, trapezoid, round, oval or the like.